sheep: change a prototype of process_main() for obtaining sender information
revive lock operation
sheep: add a list for storing information of all clients

Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
associate client info and locked vdi

Conflicts:
	sheep/ops.c
release vdi when client leaves

Conflicts:
	sheep/sheep_priv.h
support shared lock state

Conflicts:
	sheep/sheep_priv.h
	sheep/vdi.c
shared state transfer mechanism
tests/functional: add a new test for iSCSI multipath functionality